Recently, the Federal Motor Vehicle Safety Standards (FMVSS) adopted a new rule establishing two new Safety Standards, 49 C.F.R. Parts 571.403 and 571.404, relative to vehicles equipped with wheelchair lifts.1 The National Highway Traffic Safety Administration (NHTSA) authored the new Standards, which become effective Dec. 27, 2004. Although the new Safety Standards specify numerous requirements that lift manufacturers and vehicle manufacturers must comply with, the specific mandate to restrict movement of certain lift operating devices when occupied by a passenger or mobility aid, presented a new challenge to lift manufacturers. 1 The first safety standard, promulgated in FMVSS No. 403, entitled Platform Lift Systems for Motor Vehicles, establishes minimum performance standards for platform lifts designed for installation on a motor vehicle. The second safety standard, promulgated in, FMVSS No. 404, entitled Platform Lift Installations in Motor Vehicles, places specific requirements on vehicle manufacturers or alterers who install the lifts on new vehicles. Under this final rule, lift manufacturers will have to certify that their lifts meet the requirements of FMVSS No. 403, and manufacturers or alterers of new vehicles will have to ensure that the lifts are installed according to the lift manufacturer's instructions by certifying compliance with FMVSS No. 404. Federal Register/Vol. 67, No. 249/Dec. 27, 2002/Rules and Regulations/Page 79416.
The new FMVSS requirements relative to “passenger detection” are paraphrased below. For the complete text, refer to FMVSS No. 403, including the referenced tests required to verify compliance with the Safety Standard.
1. An interlock is required to prevent operation of the outboard barrier from the extended ramp position to the upright barrier position while at the ground or sidewalk level loading position if the outboard barrier is occupied by a passenger or mobility aid. See reference FMVSS No. 403, S6.10.2.6.
2. An interlock is required to prevent operation of the inboard roll stop from the extended bridge position to the upright roll stop position while at the vehicle floor level loading position if the inboard roll stop is occupied by a passenger or mobility aid. See Reference FMVSS No. 403, S6.10.2.7.
Existing sensor technologies, such as switch-mats, ultrasonic sensors, or infrared sensors, used to detect a passenger on the lift platform in order to prevent an occupied lift from stowing, are not well suited for the purposes specified in the new Safety Standard due to the physical design constraints of the lift's outer barrier and inner roll stop.
The problems associated with using switch-mat technology to comply with the new Safety Standards include at least the following:
1. With respect to the outer barrier and inner roll stop:                a. The outer barrier functions as a ramp and the inner roll stop functions as a bridge for lift platform ingress and egress at the ground level loading position and the vehicle floor level loading position, respectively. Existing standards, as well as the new Safety Standards, specify requirements limiting vertical surface transitions. Switch-mats range in thickness from 0.31 to 0.50 inches. Consequently, the use of switch-mats will exceed the operating profile of these devices.        b. Switch-mats are heavy. Adding the weight of a switch-mat to the outer barrier or inner roll stop will increase the power transmission requirements to operate the devices increasing the weight and cost of the wheel chair lift.        
The problems associated with using ultrasonic or infrared technology to comply with the new Safety Standards are:
1. The sensing pattern must be precise to avoid erroneous detection. Installation logistics, affecting sensing range and directional control compromise the accuracy demanded for this application of the sensor.
2. The sensor must be kept clean for reliable operation. The transit environment is dirty. Regular preventive maintenance is required to keep the sensor(s) lens clean for proper functionality.
3. Physical size precludes use on the outer barrier and inner roll stop.
In view of the foregoing, there exists a need for a wheel chair lift having moveable barriers that are pressure sensitive such that the barriers will not operate when an object, such as a passenger or mobility aid, are present on the barrier.